Work on the pharmacokinetics (absorption, distribution, metabolism and excretion) of the narcotic antagonist drug, Naltrexone, is being undertaken. In particular studies involving the distribution of the drug and its major metabolites in the rabbit, as well as the excretion of the drug and metabolites in the reproductive organ of the rabbit, are in progress. During the current year investigations into the excretion of the drug and its metabolites into semen (man and rabbit) are being undertaken. Studies of the biotransformation of the drug in the isolated perfused rat system are in progress. Studies on the absorption, distribution and metabolism of 1-alpha acetyl methadol in man and animals are in progress.